The endocytic adaptor ARH facilitates potassium conservation by regulating ROMK and BK.

Renal outer medullary K+ (ROMK) channels are essential for urinary potassium secretion, and their endocytosis prevents excessive K+ loss during dietary deficiency. The clathrin adaptor autosomal recessive hypercholesterolemia (ARH) has been implicated in mediating ROMK internalization, yet its physiological significance remains unclear, as hypokalemia is not reported in patients with type 4 familial hypercholesterolemia (FH4) who lack functional ARH. To address this, we investigated potassium homeostasis in ARH knockout (KO) mice, a model of FH4. Despite conserving K+ during dietary restriction, ARH-KO mice exhibited exaggerated urinary K+ loss when challenged with hydrochlorothiazide, consistent with compensatory upregulation of the thiazide-sensitive sodium-chloride cotransporter (NCC). Immunoblotting revealed significantly higher ROMK and large-conductance Ca2+-activated K+ channel-α (BKα) protein levels in the renal cortex of ARH-KO compared to wild-type (WT) mice at matched plasma K+ concentrations. Because BKα contains NPXY motifs required for ARH binding, we confirmed ARH directly associates with BKα by coimmunoprecipitation. Under potassium-deficient conditions, ARH-KO mice showed impaired downregulation of apical ROMK and BKα, indicating ARH-dependent endocytosis. Interestingly, compensatory mechanisms differed by sex: female KO mice exhibited enhanced NCC abundance and phosphorylation, whereas male KO mice showed reduced epithelial sodium channel (ENaC) cleavage and diminished BK auxiliary subunits relative to WT. These findings 1) establish ARH as a key regulator of ROMK and BKα trafficking in the distal nephron, 2) reveal sex-specific compensatory mechanisms that preserve potassium balance, and 3) underscore the delicate nature of K+ homeostasis upon ARH deletion, with maintained normokalemia at the expense of physiological trade-offs involving altered sodium handling.NEW & NOTEWORTHY Renal outer medullary K+ (ROMK) and large-conductance Ca2+-activated K+ channel (BK), both regulated by the clathrin adaptor autosomal recessive hypercholesterolemia (ARH), play essential roles in maintaining potassium balance. Given the life-threatening risks of dyskalemia, it is unsurprising that their activity is controlled by multiple mechanisms, though not without physiological costs. We found that impaired ARH-mediated ROMK and BK internalization triggers activation of alternative potassium-conserving pathways in a sex-specific manner. In females, who are more prone to hypokalemia, this compensation involves thiazide-sensitive sodium-chloride cotransporter (NCC) upregulation, a key player in blood pressure regulation.